1. Field of the Invention
The present invention relates to filler metal alloy compositions, and more particularly, to filler metal alloy compositions capable of improving appearance of a welded zone, and fluidity, penetration, etc., of an inexpensive filler metal by minimizing a content of silver (Ag) and adding tin (Sn) and silicon (Si) components.
2. Background of the Related Art
In general, welding is classified into fusion welding and soldering (or brazing) using a filler metal, and pressure welding without use of a filler metal.
Here, the fusion welding and the soldering are used to join parent metals by interposing a filler metal between the parent metals.
In addition, the fusion welding is a method of melting and joining welding zones of the parent metals and the filler metal, and the soldering is a method of melting only the filler metal and joining the parent metals, without melting welding zones of the parent metals. The soldering is based on a soft solder having a low melting point, and the brazing is based on a hard solder having a relatively high melting point.
Among filler metals used in the fusion welding, soldering and brazing, a silver solder is a typical precious filler metal, which has a lower joining temperature than other filler metals and a small heat-affected zone in the parent metal.
Further, since the silver solder has easy and good joining characteristics to various materials, the silver solder is widely used to join electronic devices, and large members such as industrial machines, and equipment.
Basic composition of such a silver solder is a ternary system of Ag—Cu—Zn, and alloys having Cd, Ni, Sn, In, Mn, or the like added thereto have been developed according to purposes such as workability, joining strength, corrosion resistance, and so on.
This silver solder is formed of, for example, a filler metal alloy composition of the Ag—Cu—Zn system used to braze coolant circulating pipes. The filler metal alloy composition of the Ag—Cu—Zn system used to braze coolant circulating pipes is added with In so as to be able to reduce a melting point of such a brazing alloy and increase fluidity thereof.
Specifically, the conventional filler metal alloy composition includes 30 to 40 wt % Ag, 34 to 38 wt % Cu, 33 wt % Zn, and 1.2 wt % In.
In particular, the conventional filler metal alloy composition including 30 wt % Ag, 35.8 wt % Cu, 33 wt % Zn, and 1.2 wt % In is widely used. Meanwhile, the filler metal alloy composition is applied to a welding rod for brazing coolant circulating pipes. Here, the coolant circulating pipe is a typical steel pipe coated with Al and Zn.
However, the Al—Zn coated steel materials provide bad joining characteristics to the welded zone when they are joined by the welding rod formed of the conventional filler metal alloy composition and when the same materials, i.e., the Al—Zn coated steel materials are joined with each other, due to characteristics of the materials.
Moreover, even when the Al—Zn coated steel material is joined not with the same material but with a different material, the Al—Zn coated steel material cannot provide good joining characteristics.
Therefore, when the Al—Zn coated steel pipes are joined by the brazing, a buffing process must be previously performed to grind the coated portion as a pre-treatment process.
Here, the buffing process is a process of grinding the surface of the Al—Zn coated steel pipe, which is performed until the surface of the coated steel pipe arrives at a state in which the joining can be properly achieved, through multiple buffing operations.
As described above, the conventional filler metal alloy composition is added with In to reduce a melting point of the brazing alloy and increase fluidity thereof, and Ag is added at 30 wt % or more.
However, a high content of expensive silver added to the conventional filler metal alloy composition may increase manufacturing cost thereof.
Moreover, when an expensive rare metal, In, is added, the manufacturing cost is further increased.
In addition, in the conventional filler metal alloy composition, since a temperature at which Zn is added is about a boiling point, Zn having a high vapor pressure may be vaporized.
Further, the vaporization of Zn may badly affect an operator's health, and a welding operation using a welding rod formed of the conventional filler metal alloy composition may badly affect the operator.
Furthermore, the operator may be badly affected while the welding is performed by the manufactured filler metal.
In addition, a large amount of oxides in a melt may cause slag during a process of manufacturing a conventional filler metal, and heating of filler metal billets to a high temperature during extrusion of the billets may cause severe oxidation scales, so that wastes are generated after the extrusion and the surface of the filler metal may be discolored after acid pickling.